1. Field of the Invention
The present invention relates to X-ray generators, and more particularly to X-ray generators incorporating a corona field cathode.
2. Description of the Prior Art
The physical mechanism involved in the production of X-rays is typically associated with electron transitions, i.e., the electromagnetic radiation that accompanies electron transition from one energy state to another. The origin of X-rays, is therefore mainly outside the nucleus, being based primarily on electron motion.
Based on these physical effects the prior art X-ray tube typically includes an electron source (cathode), a target (anode), a high voltage source to drive the electrons from the cathode to the anode, and a heating source to excite the cathode. These are all combined in a device, the X-ray tube, in which the electrons emitted from the cathode strike the anode, emitting broad band X-rays while decelerating and occasionally ejecting some of the anode electrons from the anode atoms, thereby forming electron vacancies. Electrons from higher energy states then makes transitions to fill the vacanies, transitions which are accompanied by the emission of photons of a characteristic frequency depending on the cathode material. Thus the prior art device generates X-ray photons.
The physical demands of an X-ray device, as typically implemented, are rather severe. For example, the typical voltage levels of prior art X-ray tubes are in the magnitude of 100 KEV. Even at these high voltages, shaping of the mechanical elements is extremely critical and subject to erosion and the cathode, quite often, has to be heated to temperatures commonly around 2500 degrees Kelvin. As a consequence present X-ray generation is difficult and expensive, demanding extreme tolerances in fabrication and installation. Some of these difficulties have been resolved by cathode shaping, such as the cathode shaping taught by Rogers et al. in U.S. Pat. No. 3,735,187. The teachings of Rogers et al, while suitable for their purpose, nonetheless are prone to erosion and techniques for reducing the effects of electrode erosion have been sought in the art.
A technique simplifying X-ray production in a device which is virtually immune from erosion is therefore sought in the art. Such a technique is disclosed herein.